The part of the containers which is mechanically the most fragile is the base. Indeed it is the base which supports the weight of the column of liquid contained in the container and it can lose its shape (in particular sagging of its central part) over a period of time which varies in length depending on the ambient conditions (temperature, humidity, insulation, etc.) of storage of the containers: the containers can then no longer rest on a support in stable manner.
The sagging of the central part of the container base modifies the position and/or the inclination of the walls defining the feet in the direction of the axis of the container. Thus the feet lose their orientation approximately parallel to the axis of the container and, due to the fact that the feet have in radial cross-section a curved contour, their area resting on a support moves about over their surface. The container no longer rests on a plane support in stable manner.
Retailers distributing carbonated liquids packaged in containers made of thermoplastic material such as PET in countries with severe climatic conditions (high temperature, high humidity level) wish to be able to store the containers for a long enough period of time without the containers losing their stability.
Moreover, the container manufacturers wish to be able to satisfy retailers' requests without this resulting in a reduction in the production rate of the containers, or on the contrary if possible even to further increase production rates.